A wide range of photographic developers are available in both ready-to-use solutions and compounded forms. The compounded forms are liquid concentrates, which have only to be diluted with water to obtain a working strength solution, and powder types which have to be dissolved in solution. Both the ready-to-use and compounded forms present some individual problems ranging from difficulty of uniform mixing of components in the compounded forms to the high cost of shipping the extra weight of water volume in a ready-to-use solution.
The ready-to-use photographic developing solutions are very convenient, but their large size makes shipping more expensive, and the containers take up valuable storage space. To overcome these disadvantages, there has been a trend to reduce the size of the packaging, and thus saving on the shipping cost. One way to achieve this goal is to make either an all-powder developer or a liquid concentrate developer.
Typically, powder mixes are dissolved and brought to working strength with the addition of water. However, powdered photographic developers can be difficult to dissolve, especially if caking of the powder components occurs. In certain circumstances the solution may need to be heated to increase solubility of the components and to form a completely homogeneous solution. Furthermore, in some types of powder mixes it is necessary to package the components separately because of possible interactions between alkali constituents and the developing agents.
Liquid concentrates are an alternative to the powder mixes, but because of the higher water volume they are more expensive to ship than the powder mixes. While, a higher degree of concentration will reduce some of the volume of water it also presents several additional problems. Because of the high dilution required to obtain working strength solutions, the concentrates usually contain maximum levels of photographic processing ingredients. In fact, in a highly concentrated liquid developer solidification of the components can be encountered during shipping, storage, or temperature extremes. The solidification forms a rock hard layer which is practically impossible to remove from the packaging material and makes it difficult to effect re-solution of the concentrate.
Typically, in the preparation of a liquid concentrate the mixing order of the components is not considered critical. The developing agent is not usually added until late in the mixing process to protect the developing agent. But, this can present a problem with homogeneity in the concentrate because the developing agent will not always dissolve in a solution which may be saturated with previously added photographic processing components. Instead, the developing agent will form large undissolved chunks that float on the surface of the concentrate and make subsequent diluting of the liquid concentrate quite difficult.
Accordingly, there is a need for improved concentrated liquid developers which can be shipped economically and require minimal storage space, without undergoing solidification of the active components and which can be easily reconstituted by the user.